1. Field of the Invention
The present invention relates to hydraulic shock absorbers. More specifically, the present invention relates to a method and apparatus for increasing the performance of hydraulic shock absorbers by providing acceleration sensitive damping through the regulation of fluid flow within the shock absorber.
2. Description of the Related Art
Shock absorbers are commonly used in vehicle suspension systems to absorb unwanted vibrations which occur during driving. Specifically, shock absorbers are generally connected between the body (sprung mass) and the suspension (unsprung mass) of the vehicle to "dampen" vibrations transmitted from the suspension to the body.
Vehicle shock absorbers usually have a hollow cylinder defining an internal chamber, which is divided into a compression compartment and a rebound compartment by a piston assembly slidably positioned in the internal chamber. The shock absorber includes internal valving which permits fluid to flow between the compression and rebound compartments as the piston moves within the internal chamber. One end of the cylinder is closed and is typically connected to the vehicle suspension by a suitable linkage. A piston rod extends through a seal assembly mounted in the other end of the cylinder and has its inner end connected to the piston and its outer end connected to the vehicle body by a suitable connector.
The piston assembly limits the flow of damping fluid within the internal chamber of the shock absorber during compression and extension of the shock, thereby providing a damping force which "smooths" or "dampens" vibrations transmitted from the suspension to the body. The damping characteristics of a shock absorber are determined by the fluid pressure differential across the piston required to drive the fluid between the compression, rebound and reservoir compartments. This pressure differential and resulting flow rate, in turn, controls the speed at which the piston may move in the cylinder responsive to the external forces applied to the shock absorber. The greater the degree to which the flow of damping fluid is restricted by the piston assembly, the greater the damping forces which are provided by the shock absorber. Accordingly, a "soft" compression and rebound stroke is produced when the flow of damping fluid in the working internal chamber is relatively unrestricted. By contrast, a "firm" compression and rebound stroke is produced when there is an increased restriction in the flow of damping fluid in the working internal chamber.
Different driving characteristics, such as ride comfort, vehicle handling, and road holding ability depend on the amount of damping force provided by the vehicle's shock absorbers. The amount of damping force required to meet a particular set of driving characteristics is, in turn, dependent on driving surface conditions. There are sudden and short-lived driving conditions which call for increased damping. For example, a pothole results in a rapid rebound stroke followed by a jarring compression stroke. The jarring is in part caused by an unnecessarily large rebound stroke due to the rapid falling of the suspension into the pothole. There exists a need in the art for a shock absorber with damping that adjusts automatically in response to inordinately rapid accelerations of shock absorber components.